As computer technology progressed in recent years, so-called multimedia personal computers of various types have been developed. A personal computer of this type can reproduce not only text data and graphics data but also full-motion video data and sound data.
Normally, full-motion video data is compressed and coded using MPEG1 (Moving Picture Image Coding Experts Group Phase 1; image format (at 30 frames per second): 350 pixels.times.240 pixels or less; coded data rate: 1.5 Mbits per second or less; coded image: frame image; motion vector prediction method: interframe prediction) and stored in a CD-ROM or the like. To decode and display/reproduce the full-motion video data, a dedicated expansion board is used. As an expansion board for decoding and displaying/reproducing the full-motion video data, for example, "Reel Magic" available from Sigma Designs, Inc., U.S.A., is well known. This "Reel Magic" has a video decoding function complying with the MPEG1 standard. The decoded full-motion video data is synthesized with VGA graphics received from a video card through a feature connector, and is displayed.
However, MPEG1 is a standard based on an assumption that a CD-ROM having a data transfer rate of about 1.5 Mbps is used. For this reason, in processing full-motion video data including a large quantity of image information, e.g., a movie, the image quality is undesirably degraded.
Recently, therefore, storage media of a new generation having a data transfer rate several to ten-odd times that of a CD-ROM have been developed. As such a new-generation storage medium, a system capable of recording digital data in an information amount of about 10 GB in a single disk, and realizing a data transfer rate of about 10 Mbps at maximum has been proposed as a media player.
This media player records full-motion video data or sound data which is digitally compressed and coded on the basis of the MPEG2 (Moving Picture Image Coding Experts Group Phase 2; image format (at 30 frames per second): 720 pixels.times.480 pixels or less; coded data rate: 15 Mbit per second or less; coded image: frame image or field image; motion vector prediction method: interframe prediction or interfield prediction) standard in a disk medium such as an optical disk, decodes the full-motion video data with sound data, and outputs the data to a TV set.
This media player has a disk drive unit, a data buffer, a video decoder, an audio decoder, an NTSC encoder, and the like. In this media player, an optical disk is driven by the disk drive unit, so that the full-motion video data and the sound data are read from the optical disk and stored in the data buffer.
The full-motion video data and the sound data, which are stored in the data buffer, are decoded by the video decoder and the audio decoder, respectively. The full-motion video data decoded by the video decoder is converted into an NTSC signal by the NTSC encoder and sent to the video input terminal of the TV set. On the other hand, the sound data decoded by the audio decoder is D/A-converted and thereafter sent to the audio input terminal of the TV set.
The data transfer rate of this media player is as high as about 10 Mbps, as described above. For this reason, by using this media player, movie information including not only a main picture but also a sub-picture such as a subtitle and a plurality of sound channels can be recorded in a single disk with a size almost the same as that of a CD. In addition, the main picture, the sub-picture, and the sound can be synchronized and reproduced on a TV set.
However, when this media player is to be mounted in a personal computer, a video decoder and the like must be arranged in the system of the personal computer, independently of the media player.
This is because the video decoder in the media player is dedicated to the player, so the video decoder in the media player cannot be used to decode an MPEG title recorded in a medium other than that in the media player, e.g., a hard disk or a CD-ROM.
For this reason, when a system in which a media player is mounted in a personal computer is constructed, two video decoders for reproducing full-motion video data are provided in the system, resulting in an increase in cost of the entire system.
It is an object of the present invention to provide a computer system capable of realizing an optimum system for reproducing large-capacity multimedia information including a main picture, a sub-picture, and sound data on a personal computer, thereby performing inexpensive and high-quality full-motion video reproduction without providing two video decoders for reproducing the full-motion video data in the system.
It is another object of the present invention to provide a computer system capable of decoding and reproducing large-capacity multimedia information including a main picture, a sub-picture, and sound data with a simple hardware configuration.